Propeller



J. SQUIRES Dec. 19, 1933.

PROPELLER Original Filed May 20. 1930 .INVENTOR J'ofrn Squires.

- ,L AMV ATTORNEYS- Patented Dec. 19, 1933 1,940,333 PROPELLER.

John Squires, Hagerstown, Md.

Original application May 20, 1930, Serial No.

454,138. Divided and this application October 23, 1931. Serial No. 570,663

Claims.

This invention relates to an improved metal propeller blade of the type used in propellers of aircrafts and the like and disclosed in my copending application Serial No. 454,136, filed May 5 20, 1930, of which this is a divisional application.

The main objects of the invention are to provide improved blades of this character which have a hard exterior surface capable of withstanding erosion-by the elements and particular- 0 ly by the particles of dust, dirt and other foreign matter of an abrasive nature with which aircraft propellers contact during operation; to provide a hard exterior surface of this character which is highly resistant to corrosion; to provide exterior layers of hard rust resisting material on propeller blades which tenaciously adhere to the metal body portions of the blades; to provide protective layers of this kind which, though extremely hard have a sufficiently duc- 29 tile union with the metal of the body portion of the blades to resist chipping or spalling off from the latter; to provide protective layers'of this character which vary in concentration of hard rust resisting ingredient froma maximum at the 5 outer surfaces of the blades to a minimum intermediate the thickness of the walls of the blades; and to provide a protective coating on propeller blades that gradually-blends into the metal of the wall structure thereof and avoids the forma- 30 tion of distinct layers of metal having radically different coefficients of expansion and degrees of ductility at their junction.

Further objects of the invention are to provide integral enveloping protective sheathings on steel propeller blades that may be formed without heating the metal of the blades above itsgcritical temperature; to provide integral external sheathings of this kind on propeller blades which include inherently hard compositions of iron that do not require heat treating and quenching in order to obtain the desired hardness; to provide integral enveloping sheathings on propeller blades which include as a hard constituent, main- 1y nitride of iron; to provide hard rust resisting,

outer layers onpropeller blades which are capable of being conveniently and economically produced on steel propeller blade blanks; and to provide nitrided propeller blades which are not changed in appearance by weather or other conditions to which propellers are exposed.

An illustrative embodiment of the invention is shown in the accompanying drawing, in which;

Fig. 1 is a longitudinal section of a propeller blade blank of the type from which my improved propeller blades are formed.

taken on line 44 of Fig. 3, showing diagrammatically the penetration of the nitride con stituent and the varying concentration thereof throughout a portion of the thickness of the blade.

In my copending application for Letters Patent of the United States, filed December 20, 1928, Serial No. 327,227, now Patent No. 1,831,373, dated November 10, 1931, I have disclosed the idea of case hardening the exterior surface of a hollow steel propeller blade whereby to stiffen the construction and render the propeller less liable to destruction from contact with the elements or foreign matter.

While I have found that such case hardening of the exterior surface of such blades materially enhances the life and strength of the blades, I have discovered, in accordance with the present invention, that if instead of case hardening the exterior surface of the blades, such surface is nitrided, a surface is obtained which is equally resistant to the destructive erosive action of the elements thereon and which is also resistant to corrosion. Such nitrided surface is therefore much more suitable in blades of this type than a case hardened surface. The nitrided protec tive coating or sheathing resists chipping off or spalling much more successfully than does the case hardened surface because the concentration of the hard ingredient, iron nitride varies from a maximum at the outer surface to substantially nothing within the thickness of the wall structure of the blade. This penetration and distribution of the hard element of which the protective coating is mainly formed produces a ductile union between the metal of the body portion of the blade and the outer sheathing which is not present in case hardened articles the case hardened. layers of which have a distinct line of demarkation from the body portions thereof.

Furthermore, in nitriding the surface of propeller blades it is possible to eliminate one of the heat treatments which is required when such lades are not nitrided and when they are case hardened. This is due to the inherently hard characteristics of the compositions formed during nitriding steel which are obtainable in the absence of heat treatment and subsequent quenching, whereas case hardening merely in- .as by the methods and apparatus disclosed in my copending applications Serial Nos. 415,028 and 454,136, filed December 18, 1929 and May 20, 1930, respectively. Prior to compression of the blank 1 to blade shape the blank is provided with a wall thickness which tapers from its root end portion 2 to its closed outer end 3. The external surface of the blade may be highly polished while the blank is still of circular cross-section and ca- 'pable of being polished'during rotation. v when the blank 1 has been modified to final form it takes the shape of the finished propeller blade 4, shown in Fig. 3. The propeller blade 4 is then subjected, both internally and externally if desired. but ordinarily only externally, to a nitriding treatment which may be conducted at substantially 900 F. so as to form a hard external coating or sheathing 5 which completely envelopes the blade, the temperature maintained being sufllciently low to preserve the polished.

finish. During the nitriding treatment some of the iron is converted to iron nitride which per- -meates a substantial distance into the thickness of the wall 6 of the blade. As illustrated inFig.

4, the maximum concentration of the hard ingredient occurs at the outer surface 7 of the wall of the blade and the concentration thereof decreases gradually toward the interior of the wall of the blade. Although the thickness of the protective coating 5- may not exceed more than a few thousandths of an inch it does'not terminate abruptly leaving a distinct line of demarkation between the coating and the body portion of the blade and therefore a zone is provided intermediate the thickness of the blade which gradually decreases in hardness and provides a somewhat ductile union between the external part .of the coating 5 and the body portion of the blade that successfully resists chipping and spalling'oif of the coating from the body portion.

The nitriding treatment may be successfully performed on inexpensive grades of steel at a relatively small manufacturing cost with a result of providing an' extremely hard external surface, for instance a surface having 1000 surface of the blade, serves materially to stiffen the blade and increase its resistance to deformation. I

Although but one specific embodiment of this invention has been herein shown and described, it will be understood that numerous details of the construction shown may be altered or omitted without departing from the spirit of this invention as defined by the following claims.

I claim:

1. A hollow steel propeller blade having a nitrided exterior surface.

2. A hollow steel propeller blade having a relatively thin wall the thickness of which is reduced from the base to the tip, and the exterior face of which is nitrided.

3. A hollow steel propeller blade having a relatively thin wall the thickness of which is reduced from the base to the tip, and the exterior surface of which is nitrided to a substantially constant depth throughout.

4. A propeller blade comprising a hollow 'steel body portion of relatively thin wall section and an integral external enveloping sheathing including a composition of iron and a hardening material having rust resisting properties.

5. A propeller blade comprising a hollow steel body portion of relatively thin wall section and an integral external enveloping sheathing including a combination of steel and iron nitride.

6. A propeller blade comprising a hollow steel body portion of relatively thin wall section and an integral external sheathing including a combination of iron and iron nitride having a maximum iron nitride concentration at the external surface of said blade and a gradually decreasing iron nitride concentration toward the interior of the wall of said body portion.

'7. A propeller blade comprising a hollow steel body portion of relatively thin wall section and an integral external sheathing including a combination of the metal of said body portion and an inherently hard compoundthereof having corrosion resisting properties, the concentration of said compound in the sheathing decreasing from the exterior surface of said blade to a minimum intermediate, the inner and outer surfaces of the wall thereof.

1 8. A metal propeller blade comprising a hollow steel body portion and a hard rust resisting external layer including a combination of the metal of said body portion and iron nitride, and having an inherent characteristic hardness obtainable independently of heat treatment of the blade, the wall thickness of said blade being relatively small and said external hard layer materially stiffening said blade and rendering it resistive to corrosion and erosion.

9. An article of manufacture comprising a hollow steel propeller blade having a relative thin wall section, the exterior surface of said blade being nitrided to aid in enhancing the strength of said blade and rendering it resistive to corrosion and erosion.

10. A propeller blade comprising a steel body portion having a nitrided exterior surface.

I JOHN SQUIRES. 

